Angle modulated carrier wave detector



Patented May 17, 1949 ANGLE MODULATED CARRIER WAVE DETECTOR `George C. Sziklai, Princeton, N. J., assignordso Radio Corporation of America, a corporation of Delaware Application July 14, 1944, Serial No."544,=939

(Cl. Z50-27) 7 Claims. l

My Ipresent invention Y-r'elates generally to detectors of angle modulated carrier waves, and more particularly to a novel circuit for detecting frequencyor iphase modulated carrier waves independently of amplitude variations.

It is well-known that in the absence of special precautions the conventional frequency modulation (FM) detector not only has an output dependent on frequency deviation, but also on intensity variation vofthe signal. Even in the case of a balanced FMdetector circuit, which has zero output at carrier frequency, cross-modulation effectsare obtained if the carrier intensity changes during Aproduction -of output energy in response to frequency'deviation, i. e., simultaneously with receptionof frequency modulated signals. In the past an amplitude'limiter stage has been used prior uto the FM detector to minimize such carrier intensity changes. Limitersare, in general, clipper tubes which require a minimum signal to operate, and this 'mini-mum -signal determines the sensitivity of the'detector and of the receiver.

`One of the disadvantages of a limiter is that it has a comparatively large portion of its normally high gain diverted into amplifying carrier harmonics during actual limiting. In my Patent No. 2,408,702, `granted October 1, 1946, I have shown circuits forreceiving angle modulated carrier waves without the use of a special limiter stage prior to `the detector. In that application a tube of the so-called electron -beam type is provided with a target" element having sections thereof capable of emitting secondary electrons. In addition, the beam-tube included a special means yfor controllingl the electron beam of the tube'so as 4to Aminimize the effects of intensity variations of the received signal energy on the outputcurrent of the beam tube.

In his U. S. Patent No.-2, 344,679 granted March 21, 1944, M. G. Crosby has disclosed and claimed a detector for angle ymodulated carrier waves comprising a beam type tube whose operation is independent of 4amplitude variation of the applied angle modulated carrier waves. In the Crosby system la 'plurality of output or anode quadrants are futilized to collect electrons from a beam subjected to deflection by two signal voltages whoseiphase differences are to be detected.

It may-be statedvthat it is an important object of my present invention toutilize a detector of the general Atype disclosed by Crosby, but, in addition, utilizing as the actual output electrode of the'beam tube :a target velement embodying features generally ldsclosed'iin my aforesaid application.

In my aforesaid application azpair of deiiection plates functioned fto-provide'control voltages for sweeping anl :electron-beam .over a non-uniform secondary electron emission y.areaof the output electrode of the :beam tube. Another important object of my present invention is `to simplify the detector of my aforesaid application by .utilizing as the output .electrode thereof =a circular target having secondary emissionlsectors or .quadrants of alternately different .emissi-vity.

Another object -ofmy invention is to provide an improved lphasefdetector employing a beam tube having a deecti-ng -an'd 'target' system that is inherently non -responsive to amplitude changes, and the target-being soconstructed that a relatively 4high 'impedance' maybe satisfactorily employed-as theloutputfielement whereby ahigh modulation voltage output level is provided.

A more specic yobject of my 'invention is to provide a beam tube for use in rdetecting angle modulated carrier =wave`s; the output electrode of the beam tube being Adivided into four sectors, two of the sectors being diametrcally opposed and being coated with -a material `of lowsecondary emissivity, andthe remaining -two opposed sectors being'coatedwitha :material of relatively high secondary .emissivity Further objects ofmyinvention Yare lto improve generally 'beamtube circuits forthe detection of FM or .PM carrier waves, Iand more particularly to .provide such .circuits in an eicient and economical manner.

While I have indicated and ,described several systems for carrying my invention into effect, it will be apparent to .one skilled in .the art that my invention is .byno means limited to the particular organizations shown .and described, but that many mod-ications 'may b e made without departing from the scope of .my invention, as set forth in the appended claims.

In the drawing:

Fig. 1 shows .an detectorsystem embodying the invention, .the beam tube lenvelope being broken away to kshow thetube' interior;

Fig. 2 illustratesideal':resonance curvesof the discriminator section of `the .FM detector;

Figs. 3a, 3b, Scand dshowrespectively different appearances `of the electron tracesfpatterns or figures yformedon the output or .target electrode;

Fig. 4 rgraphicallydepicts gthe eiiectivc .voltage levels of theioutput 'electrode -T for therespectively different fpatternsof Figs. 3a `to 3d;

Fig. wgraphicallygshows-fthe `wave .form of `the 3 output electrode (target) voltage in response to the pattern C shown in Fig. 3c; and

Fig. 6 shows a modification of the target T used in my invention.

Referring now to the accompanying drawing, wherein like reference characters in the different figures designate similar circuit elements, the tube l will rst be described before explaining the nature of the electrical circuits of the phasing (or discriminator) network which furnish the control voltages for the deiiection electrodes. The tube l may generally be of the well-known cathode ray oscilloscope type. The tube envelope may be made of glass or metal, and is suitably evacuated. A suitable source of electrons, indicated by numeral 2, s connected to ground. The electron emitter 2 may be a cathode or gun of the indirectly-heated type, and is adapted to project or emit a stream of electrons in the form of a beam 3. The beam 3 is schematically represented by a dotted line.

It will be understood by those skilledin the art of cathode ray tube construction that suitable focusing electrodes may be positioned along the path of beam 3 to maintain the normal beam formation along a 'line terminating at the center of the disc-like target or output electrode T. The numeral 4 designates such a focusing electrode. The electrode fi is a disc provided with a central aperture through which the beam 3 passes. The electrode d is positively biased relative to the grounded electron emitter 2, and, hence, the electrode Il functions as a beam-forming electrode. Of course, additional beam-forming electrodes could be interposed between electrode li and the deflection electrodes. Further, the invention is not restricted to the specific configuration of electrode t.

The beam 3 normally passes between, and along the central axis of, two pairs of equidistantly spaced deflection plates 5-5 and 5 5. The spacing between the plates of the respective pairs is equal, and the planes of plates in different pairs are normal to each other. The deflection plates form a deecting or control area over beam 3 which normally passes along a median line relative to the four plates. Although the deflection plates are shown at the same point along the electron beam, it is to be understood that one pair of plates (say 5-5) may be positioned closer to the electron emitter 2 than the other pair as is often done in cathode ray oscilloscopes.

The electrode E is a high voltage, electroncollector electrode. t is shown as consisting of a plurality of concentric metallic rings all conductively connected to each other and to a source of positive potential. The potential of electrode E is highly positive relative to the potential of electrode 4. Four plus signs (+|-|-l-) are employed to indicate that collector E is highly positive; this is a purely illustrative representation. The electron beam 3 normally passes through the center of the smallest ring, but the beam is capable of passing through the inter-ring spaces in response to appropriate deflection of the beam.

The target or output electrode T is metallic, and is shown as having a circular configuration. The target is spaced from the end of the tube, although it may be provided as a coating on the inner face of the end of the tube. The target is divided into four effective quadrants or sectors. The sectors are of equal area, and comprise two pairs of diametrically-opposed, secondary electron emission surfaces of different characteristics. Thus, sectors 'l and 'I' are of like secondary electron emissivity, and are capable of emitting a copious flow of secondary electrons upon bombardment by the beam of primary electrons 3. The second pair of sectors 8 and 3 of like emissivity are capable of emitting a relative weak now of secondary electrons in response to bombardment by primary electrons of beam 3. By way of specific example, sectors 8 and 8' may be coated with carbon to provide surfaces of low secondary emission ratio. The sectors l and 'l' may be coated with caesiurn oxide to provide surfaces of high secondary emission.

The diameter of target T may be substantially greater than that of collector E so that all the primary electrons passing through the collector inter-ring spaces will impinge on the target. It is to be clearly understood that the invention is not limited to the specific configurations of electrodes E and T. Further, the specific materials described above for the high and low secondary emission surfaces need not be employed, but may be replaced by any other suitable materials capable of functioning as required.

When the beam 3 is deflected in such a way that the electrons thereof land on the low secondary emission surfaces 8 and 8 of target T, only a relatively small number of secondary electrons leave the target. On the other hand when the beam is deflected so that its electrons hit the high secondary emission areas 'l and l', a large number of secondary electrons leave ythe target. The target is normally maintained at a positive potential which is substantially less than the voltage of collector E. The direct current source 9 is shown as having its negative terminal grounded, while the positive terminal -l--l--lis connected to target T through a resistor R of high impedance value. The condenser Il? bypasses the direct current source G to ground. It may have a value of 0.5 to l0 microfarads, and may be omitted if desired. Normally, and with no alternating voltage applied to deflection plates 5, 5 and 6, 6', the electron beam 3 lands at the center of the disc T, i. e., at the intersection point of the sector division lines.

I have shown the cathode ray tube l connected in an FM receiver to function as an FM detector. The FM receiver is assumed to be a superheterodyne receiver employed in the 42 to 50 megacycle (Inc.) band, the present FM broadcast band. In that band each carrier frequency is varied at the transmitter in accordance with modulation signals. The extent of frequency variation is a function of modulation signal amplitude, while the rate of variation is dependent upon the modulation frequencies per se. The permissible frequency variation or swing, in accordance with present broadcast transmitting standards, is a maximum of 75 kilocycles (kc.) to each side of the carrier frequency. My invention is not restricted to the FM range of ll2-50 mc., nor to FM reception, nor to the specic overall frequency swing of kc. The term angle modulated carrier wave used in this application includes phase modulated (PM) carrier waves, FM carrier waves, or hybrid modulations of PM and FM possessing characteristics of each. At the receiver it is desirable to prevent so far as possible the appearance of amplitude modulation (AM) on the received Icarrier wave so as to preserve the correspondence between the original frequency modulation of the transmitted wave and the modulation output of the detector. In the aforesaid Crosby patent it has been shown that the beamv tube inherently prevents amplitude modulation (AM) in the received wave from affecting the detector output current.

The numeral I2 in Fig. 1 designates an ampliiler preceding the usual discriminator network feeding tube I. Amplifier I2 may be a non-limiting amplier of intermediate frequency (I. F.) signals whose input electrodes are coupled to a prior I. F. ampliiier, or to a converter. Of course, amplifier I2 may be made to serve as a limiter, if desired. The networks which precede I. F. amplifier I2 are of suitable and well-known construction. They may comprise a signal collector and one or more selective high frequency amplifiers followed, if the receiver is of the superheterodyne type, by a converter which functions to produce the I. F. signal energy. The I.,F. value may be chosen from a range of 2 to 15 mc., as for example 4.3 rnc. My invention is not limited, however, te any specific I. F. value.

The amplifier I2 amplifles the I. F. signal energy at the 4.3 mc. value. In the plate circuit of amplier I2 there is arranged a resonant circuit I3 tuned to the selected 4.3 mc. value. The low potential side of circuit I3 is connected to the B+ terminal of a suitable direct current energizing source, while condenser I4 bypasses I. F. currents to ground. The primary circuit I3 is magnetically coupled to a pair of separate secondary circuits ld and It. The secondary circuits are preferably free of coupling therebetween. The junction of the secondary circuits I5 and I6 is established at ground potential for I. F. currents. The circuits i5 and i6 are tuned to respectively opposite sides of the I. F. value, and the frequency spacings between the resonant frequency of each secondary circuit and the primary resonant frequenct (4.3 mc.) are preferably equal.

In Fig. 2 I have graphically represented idealized resonance curves of secondary circuits I5 and Iii. Circuit I5 has a peak frequency of 4.2 mc., while circuit IS has a peak frequency of 4.4 mc. substantially in excess of the overall maximum frequency swing of 150 kc. The curves of Fig. 2 cross over at 4.3 mc., the center frequency (Fe) of applied I. F. signal waves. The circuits I3, I5 and Iii provide a form of frequency discriminator of well-known characteristics. My invention is not limited to this specific form of discriminator, since the discriminator shown Iby S. W. Seeley in his U. S. Patent No. 2,121,103, granted June 21, 1938, may be used to supply the deflection voltages for tube I. Reference is made to the aforesaid Crosby patent for a disclosure of other forms of frequency, or phase, discriminators that may be employed to energize deflection plates 5, 5 and 6, 6'.

The functioning of the discriminator of the present application is Well-known. Instantaneous deviations of frequency from the center or reference frequency Fe (the I. F. value) cause corresponding increases or decreases of signal voltage across the respective secondary circuits I5 and I6. For example, should the frequency of the signal energy instantaneously deviate to 4.2 mc., there will be maximum radio frequency voltage built up across the circuit I5 while minimum voltage exists at circuit I6. Conversely, an instantaneous shift of signal frequency to 4.4 mc. results in maximum radio frequency voltage being developed across circuit I G, with minimum voltage across circuit I5. At the value Fc the voltages across circuits I5 and I6 are equal.

Hence, by connecting plate 5 to the high potential Hence, the peak spacing is 200 kc., which is side of circuit I5 and vopposite plate 5 to ground, any radio frequencyvoltage across circuit I5 will be applied between plates 5 and 5. Similarly, the plate 6 is connected to the ungrounded side of circuit I6, while plate 6 is grounded. Hence, voltage across circuit I6 is applied between plates 6 and 6'.'

Accordingly, the amplitude variations in the voltages across circuits I5 and I6 are respectively applied to deflection plates 5, 5 and 6, e. The variations in deflection voltage control the electron beam 3, and cause the beam to sweep or trace figures or patterns over the inner face of target T. It will now be seen that the discrimiv nator network derives from the angle modulated carrier Waves (specifically FM carrier waves) a pair of radio frequency voltages Whose relative amplitudes are a function of the direction and degree of angular deviation of the waves relative to a reference phase or frequency value, and that the pair of voltages are employed to control the path of an electron beam normally positioned to impinge the target T at the center thereof.

In Figs. 3a, 3b, 3c and 3d I have shown, in a purely illustrative and idealized manner, the various electron patterns or traces formed on the target T by the beam 3. When the frequency of the I. F. signals at circuit I3 deviates to a frequency of 4.4 mc., the resonant frequency of circuit IB, the voltage between plates t and t' will -be a maximum, and the voltage between plates 5 and 5 will be substantially zero. This results in the horizontal trace A of Figure 3a, since the electron beam 3 will be deflected between the horizontal plates 6 and 6. and the vertical plates 5 and 5 will exercise no effect on the beam. Assume, now, that the frequency instantaneously deviates to the peak frequency of circuit I5; the vertical plates 5 and 5' will then produce the vertical trace B of Fig. 3b. IIhe circular trace C of Fig. 3c will result in response to the applied signal energy having a frequency of Fc. Since the deflection voltages are necessarily equal at this center frequency, and since they are in phase quadrature as well, the electron beam will be caused to trace the circular path C over the target sectors. An elliptical trace results when the deflection voltages are unequal and the instantaneous frequency of applied signal energy is at a value between one lirriiting frequency (4.2 or 4.4 mc.) and Fc. In Fig. 3d the horizontal axis of the ellipse is greater than the vertical axis thereby signifying that the horizontal plates B and Ii have a greater voltage difference than vertical plates 5 and 5.

The electron beam patterns or traces on the target T are readily translated into variations of voltage across output resistive impedance R. The latter has a relatively high impedance. Hence, it develops a relatively high voltage drop thereacross due to current flow in the target circuit. In general, then, a relatively high gain is secured at the output terminals of detector tube I as compared with prior art detectors. The voltage variations across output resistance R, integrated by shunt condenser II, lcorrespond to the modulation of the received carrier waves and may be amplified by the modulation amplifier 2li. The latter, in the case of audio frequency modulation, is preferably coupled by resistance-capacity coupling to the output resistor R. The amplified audio frequency voltage may be utilized in any well-known and suitable manner.

Consideringnow, the manner in which the y electronbeam deflections are translated into target current variations, assume .rst that they circular trace C is 'being produced inresponse` to` the FM wave at circuit I3 having an instantaneous frequency Fc. The electron beam traverses all' of `the target sectors uniformly and at Aa uniform' rate. Hence, secondary electrons are caused to be emitted from the sectors 1, 8, 'l' and 8 inthat alternate order. Acordingly, the target output current and, consequently, the outputvoltage,l will follow the idealized square wave form shown-in Fig. 5. That the target output voltage follows the wave form of Fig. is-se'en from the Ifollowing considerations.

Duringv the time that beam 3 sweepsacrosszthe. high secondary emission sector 1 'there will be av relatively large flow of secondary electrons from. sector 'i to the highly positive collector electrode E. Hence, the target T will ybecome relativelymore positive since the electrode E diverts electron current from it and 'thereby lessens the voltage drop across resistor R. This is, also, true when the beam sweeps over sector 1. Duringthe sweep periods over 1 and l', then, the target will be highly positive, approaching the potential 4of collector E. These periods of target voltage Vare represented by the succesive square peaks of the wave form of Fig. 5. The intermediate valleys of the wave form correspond to the periods wheny beam 3 sweeps over sectors 8 and 8'.

Since the sectors 8 and 8 are low vsecondary electron emission areas, they will emit relatively few secondary electrons to collector `E in response to the primary electrons of beam 3. Thisl means that more negatively charged primaryielectrons will be arriving at target T than secondary negative electrons are lost by the target. Hence, there will be a relatively large flow of current to the target through resistor R andthe target voltage tends to approach the potentialof emitter 2` for the periods when beam 3 sweeps over sectors 18- .l

and v8. It will now -be seen that whereas lthe target current decreases sharply during periods when the beam sweeps sectors 'i and 1' with resultant sharp increase in target voltage, theltarget current increases sharply during thesweeping of sectors 8 and 8 with resultant sharp decrease in target voltage. The average voltage of target T for the entire circular trace C is depicted as a dot and dash horizontal line in Fig. 5.

The variation of target output voltage may be explained on still another basis. During those periods when beam 3 sweeps low emission sectors 8 and 8', it may be said that there exists a closed series circuit which is traced from the grounded emitter 2, through the resistive path of the beam 3 to sector -8 V(or 8') of target T, through resistor R and current source l8 backto ground. The resistance of the beam-path is very small, whereby high impedance R is in'series with thesource 9l and causes target T to approach the "potential ofemitter '2, which isat ground potential'. Attention. is directed to Fig. 4 which depicts ina purely -illustrativefashion, and ldoes not represent .absolute potentials but Acomparative `potentials, that lthe average potential levell of target T is close to ground potential' of 4emitter Zwhen beam v3l sweepsv sectors 8,18?. This is the A position of Fig. 3a.

When `the beam sweeps sectors :1, VT (position B in `Fig. 3b) vthe eiectiveoraverage voltage' of target T'is closeA tothe voltage ofelectrodeLE; Thisis shown in Fig. 4. In-thiscaseithe resistor R of the aforementioned icio-sed' series rcircuitis slnmtedlbypJ circuitzcomprising thecurrentvsource andwenergizing zelectrode Erin series with thefre- .ating channel is negligible.

8` sistive :impedance of t-the secondary electron path fromsector-l x(for 1^) to'coll'ector` E. The potential of target T is now liftedabove ground potential, and is :close to the potential of collector E.

Fig. 4lshowsfthe average. or effective .potentials oiv target. T resulting from the corresponding traces A, B, C'v and D of Figs. 3a, 3b, 3c and 3d respectively. rIhe average potential of T is depicted-.in Fig. 4. as a vdot-dash line marked Beam atv C. The elliptical trace D of Fig. 3d whose corresponding target potential level is represented -bythe line of long dashes in Fig. 4, involves Irelatively longer sweeps of sectors 8 and 8 than of sectors 1 and 1'. Hence, the average or `effective potential of target T will be more positive lthan for the A trace, but less positive than forthe C trace.

It has vbeen .found that when the electron beam sweeps over the target T it produces a narrow pulse when it passes the center of the target. EvenY when it sweeps over the target horizontally asin Fig. 3a or vertically as in Fig. 3b it produces av narrow pulse in a positive or negative sense respectively. The reason for the creation of these vpulses is believed to be that the electron beam, dueto its nite diameter, impinges on both sectors 1, 1 and 8, 8 at the central, cross-over point. Condenser H acts to by-pass these high frequency pulses, greatly above the range of audibility, which would otherwise appear across resistor R.

It is moreover preferred to choose the Values of resistor R and condenser ilso that they will have a time constant of microseconds, accordl ing topresent standards of deemphasis. If, for

example, R is 1 megohm, then C11 may be 100 micro-microfarads; if R is equal to 5 megohms then Cn may be about 20 micro-microfarads, etc.

It will bereadily seen that the deflection of the primary electron'beam, in response to variations in relative amplitude `of the applied alternating voltages arising lfrom variations Ain frequency of the received signaLwill cause corresponding electron traces or patterns-on the alternate sectors of the target T. The length of the arc sweeping one sector area orthe other of the target will charge the latter to apotential dependent on whether the pattern is mainly on sectors T, i or on sectors 8, 3'. Accordingly, variations in potential of target T are representative of the modulation which was originally applied'to the-carrier wave at the transmitter.

The system-disclosed herein is inherently nonresponsive to amplitude changes. Amplitude changesof the carrier will change'only the amplitude-of the beam sweep, but not the arc or angle. Hence, the target potential at any instant will be substantially independent of carrier amplitude changes, and', thereforemo special amplitude limiter need be used ahead of the discriminator network. The use of pairs of opposed sectors for target T permits sensitive detection to take place. The frequencyv deviation'is 'thereby translated into a high voltage gain at the detector. If desired,

Yhowever, only one sector 'I and one sector 8 may be employed. i

Myl present detector circuit is characterized by an improved adjacent channel selectivity. Thatis, the-response to signals outside the oper- The beam tube will not substantially'change its target potential, ac- -corclingtoy any modulation, save within the frequencies of-4`12 to 4.4 mc. Outside of these frequencies-.regardlessof the-presence or absence of fasign'al, :the Ytargetpotential will be constant,

'except :for :the high r`-frequency Apulses Eheretofore l-mentioned fas arising `when tthe velectron beam passes the center of thetargetfand as-being re- -moved'byfcondenser itl. `Thisfollows from the l' fact l that it' does not matter how wide the beam is swept, Vso long as itis swept-only over high, or -only over low, secondaryelectron emission areas. -In other yvords, asignaloutside the frequency band (200km) delimited by the peaks of Fig. 2-will ifabove 4.4mm ycausev'the tracepattern Ito be always on sectorsB-'BQ and ifbelow '1412 kc.

cause -the rtrace pattern to :be always 1 on sectors 1,1'. Of'course, ythese conditions would bere- -versed if -wereversed-the tuningpoints of 'circuts-i'andi. 'Even ifa-signal outside the'frequency yrangefof-*42 to '4-.4 mc. were within the admission band I of Athe circuit, it would produce equal ypulses 4as the electron beam `crossed the "centerl of 1the'v'target regardless of its amplitude or frequency. *So long `asthe pulse Ywidth does'not change, no `audio `frequency-output will beobtained. Hence, the f adjacent channel selectivity is of a relativelyhigh order of magnitude in my circuit.

In theform of my'inventionthus far yspecifically described, whenmosignal isavailable thermal agitation and `otherrandomsourcesmay give rise to voltages which cause the electron beam to make short excursions fin any 'direction from the center of the target thereby producing a noise output. -In the modification-shown in Fig. 6, I provide a small circular opening 30 at the center of the target l. Thisopening will beeof suitable diameter and will be at least slightly larger in diameter than the electron Ibeam. Accordingly,

when 1no fs'ignal `is present .or when the electron beam iis moved .only slightly .in lresponse to noise potentials, kthebeam .doesnottimpinge on theltarget, and no alternating current .voltage output arises lacross 4lresistor .R. .Of icourse, provisionlof opening ,30 .affects .the high .frequency pulses produced by the excursion of the electron beam across the center of the target. However, such high frequency pulses will still be removed by the condenser Il.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention.

What I claim is:

1. A method of translating angular modulation of a carrier wave into modulation voltages, which includes producing a beam of primary electrons, collecting the primary electrons, deriving a voltage in response to said collected electrons, concurrently producing a stream of secondary electrons in response to the collection of said primary electrons, collecting the secondary electrons thereby to affect the magnitude of said derived voltage, producing from said modulated carrier wave at least two carrier voltages whose relative magnitudes are a function of the angular modulation of said carrier wave, defiecting said primary electron beam in one direction in accordance with the relative magnitude of one of said two voltages and at right angles to said one direction in accordance with the relative magnitude of the other one of said two voltages thereby toI produce a variation in the intensity of said stream of secondary electrons whereby said derived voltage is varied in accordance with said angular modulation.

*2. lA detectorv vofrangle1nm'rlulated carrierwaves vcomprising afrequency'.discriminator network'A for `deriving *from said'wavesa first and a second Ihigh frequency voltage' whose relative'magntudes vary in accordance- -With instantaneous frequency deviations'o'f said waves relative to the center 'frequencythereof,-a cathode raytube including an emitter 'of a'primaryielectron stream, a target arranged tobetraversed by said electron stream `and'having at least two areas of substantially different secondary electron` emission ratio, an: electrodefor collectingisecon'dary electrons liberated `from said vtarget, 'deflectorsjcoupled to said 'frequency discriminator networkand constructed so asi to 'deflect'said 'electron stream in one direction inaccordance with sadrst voltage and at right anglesito said'one'direction in accordance with said `second voltage," andan `outputcircuit includingy an impedance element effectively connected between saidtarget'andsaid vcollector electrode for developing 'an outputvoltage representative of they modulation of lsaid` waves.

3. A detector of angle modulated carrier Waves comprising a frequency discriminator network for deriving from said waves a flrstand a second high frequencyvoltage whose relativemagnitudes vary inaccordance withinstantaneous frequency deviations lo'f'said wavesrelativeitol the centerfrequency 4thereof, a 'cathode ray tube including an emitter-of aprimary electron stream, .a target arrangedto be traversedby'sai'd electron stream and having 4four sector-shaped areas, v'alternate areas' of V`said target'l being 'of `substantially different secondary electron "emission ratio, an electrode vfor coliectingsecondary electrons liberated from `vsaid target, la "pair l of v'de'ilectors coupled to said -frequency discriminator network and constructed -soas-tofdeectsaid electron stream vin one 'direction yin accordance with said rst 'voltage-and at :right anglesto said one direction in accordance '-withfsaid second voltageand 1 an output circuit including an impedance element effectively connected between said target and said collector electrode for developing an output voltage representative of the modulation of said waves.

4. A detector of angle modulated carrier Waves comprising a frequency discriminator network for deriving from said waves a rst and a second high frequency voltage whose relative magnitudes vary in accordance with instantaneous frequency deviations of said waves relative to the center frequency thereof, a cathode ray tube including an emitter of a primary electron stream, a target positioned to be traversed by said electron stream and having at least two sector-shaped areas of substantially different secondary electron emission ratio, an electrode for collecting secondary electrons liberated from said target, a pair of deector elements connected to said frequency discriminator network, one of said pair of deflector elements being positioned so as to deect said electron stream in one direction in accordance with said first voltage, the other of said pair of deflector elements being positioned so as to deflect said electron stream at right angles to said one direction in accordance With said second voltage, and an output circuit including an impedance element effectively connected between said target and said collector electrode for developing an output voltage representative of the modulation of said waves.

5. A detector of angle modulated carrier Waves comprising a frequency discriminator network for deriving from said waves a first and a second high frequencyv voltage whose relative magnitudes vary in accordance with instantaneous frequency deviations of said waves relative to the center frequency thereof, a cathode ray tube including an emitter of a primary electron stream, a target arranged to be traversed by said electron stream and having at least two areas of substantially different secondary electron emission ratio, a perforated electrode between said emitter and said target for collecting secondary electrons liberated from said target, a pair of deectors coupled to said frequency discriminator network and constructed so as to deflect said electron stream in one direction in accordance with said first voltage and at right angles to said one direction in accordance with said second voltage, and an output circuit including an impedance element effectively -connected between said target and said collector electrode for developing an output voltage representative of the modulation of said waves.

6. A detector of angle modulated carrier waves comprising a frequency discriminator network for deriving from said waves a first and a second high frequency voltage whose relative magnitudes vary in accordance with instantaneous frequency deviations of said waves relative to the center frequency thereof, a cathode ray tube including an emitter of a primary electron stream, a target arranged to be traversed by said electron stream and having at least two sector-shaped areas of substantially different secondary electron emission ratio, an electrode for collecting secondary electrons liberated from said target electrode, a pair of deflector elements connected to said fre- `quency discriminator network and constructed so as to deflect said electron stream in one direction in accordance with said rst voltage and at right angles to said one direction in accordance with said second voltage, an output impedance element effectively connected between said target and said collector electrode, and an integration circuit coupled to said output impedance element for developing an output voltage representative of the modulation of said waves.

7. A detector of angle modulated carrier waves comprising a frequency discriminator network for deriving from said Waves a first and a second high frequency voltage whose relative magnitudes vary in accordance with instantaneous frequency deviations of said waves relative to the center frequency thereof, a cathode ray tube includi g an emitter of a primary electron stream, a tar et arranged to be traversed by said electron stream and having at least two areas of substantially different secondary electron emission ratio, said target having a central aperture of a diameter larger than that of said electron stream, an electrode for collecting secondary electrons liberated from said target, deectors coupled to said frequency discriminator network and constructed so as to deflect said electron stream in one direction in accordance with said rst voltage and at right angles to said on-e direction in accordance with said second voltage, and an output circuit including an impedance element effectively connected between said target and said collector electrode for developing an output voltage representative of the modulation of said waves.

GEORGE C. SZIKLAI.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,069,441 Headrick Feb. 2, 1937 2,191,185 Woli Feb. 20, 1940 2,202,376 Hansell May 28, 1940 2,305,646 Thomas Dec. 22, 1942 2,344,679 Crosby Mar. 21, 1944 2,408,702 Sziklai Oct. l, 1946 

